1. Field of the Invention
The present invention relates to a monitor for monitoring the integrity of wire bonds while conducting bonding operations. More particularly, the present invention relates to testing the pull strength of first and/or second bonds during teach or during production operations.
2. Description of the Prior Art
When automatic high speed wire bonders are set up for bonding operations, it is known to bond an interconnecting wire and then place a "J" hook of a calibrated pull tester under the wire and to pull until the wire breaks or one or more of the bonds fail. The information gained from such manual intervention destructive tests enables maintenance personnel to achieve uniform acceptable bond strength for subsequent bonding operations.
After a wire bonder is set up for production operations, it is known to monitor for missing wires and/or non-stick bonds and to monitor bond quality. Such systems are shown and described in U.S. Pat. Nos. 4,558,596; 4,808,948 and 4,586,642 all of which are assigned to Kulicke & Soffa Industries Inc., the assignee of the present application.
The aforementioned patents are directed to systems that monitor either frequency or resistance to determine the continuity of an electrical pad indicative of a bonded wire. Other systems monitor frequency or resistance to determine the bond quality. None of the aforementioned bond quality monitoring systems are known to be capable of simultaneously monitoring bond strength and bond quality. All prior art pull strength tests require operator intervention.
Gold ball bonds made at a first bond position are usually stronger than wedge bonds made at a second bond position. The trend toward higher density integrated circuits on large chips has effectively decreased the size of the lead out pads on the semiconductor chip. This trend has generated a need for smaller ball bonds and special bonding tools for making fine pitch first and second bonds. The trends towards smaller non-conventional tools have created a need to monitor the bond strength because the smaller tools wear faster and smaller bonding tools usually result in lower bond strength. Applicants do not know of an apparatus or system that will non-destructively test bond strength and monitor tool wear during a bonding operation.
Accordingly, it would be desirable to provide a novel wire bond monitoring system which cooperates with a novel wire continuity monitoring system and an adjustable force application and monitoring system to detect changes in bonding operations which affect the pull strength of wire bonds made during production operations. It would be further desirable to selectively collect wire bond pull strength data during actual production on line operations which can be used to adjust bonding parameters which in turn produce optimum bond strength.